Traditionally, ophthalmic lenses may be made by cast molding, wherein a monomer material may be deposited in a cavity defined between optical surfaces of opposing mold parts. Multi-part molds used to fashion hydrogels into a useful article, such as an ophthalmic lens, may include, a first mold part with a convex portion that corresponds with a back curve of an ophthalmic lens and a second mold part with a concave portion that corresponds with a front curve of the ophthalmic lens. To prepare a lens using such mold parts, an uncured hydrogel lens formulation may be placed between a plastic disposable front curve mold part and a plastic disposable back curve mold part.
The front curve mold part and the back curve mold part typically may be formed via injection molding techniques, wherein melted plastic may be forced into highly machined steel tooling with at least one surface of optical quality. The front curve and back curve mold parts may be brought together to shape the lens according to desired lens parameters. The lens formulation may be subsequently cured, for example, by exposure to heat and light, thereby forming a lens. Following cure, the mold parts may be separated and the lens may be removed from the mold parts.
Cast molding of ophthalmic lenses has been particularly successful for high volume runs of a limited number of lens sizes and powers. However, the nature of the injection molding processes and equipment may make it difficult to form custom lenses specific to a particular patient's eye or a particular application. Consequently, other techniques have been explored, such as lathing a lens button and stereolithography techniques. However, lathing may require a high modulus lens material, may be time consuming, and may be limited in the scope of the surface available, and stereolithography has not yielded a lens suitable for human use.
Recently, new types of ophthalmic lenses that may comprise inserts have been proposed, wherein the inserts may be incorporated into standard ophthalmic lens materials, such as a hydrogel. Current molding techniques may not be suited for manufacture such exemplary ophthalmic lenses, and the issues associated with lathing and stereolithography may be exacerbated by the addition of an insert. For example, lathing too deeply in an ophthalmic lens surface may damage an encapsulated insert.
Unlike with a standard ophthalmic lens, additional manufacturing steps may be necessary to allow the standard ophthalmic lens material to adhere or encapsulate the insert. With typical molding techniques, the stress from pulling the front curve mold part from the back curve mold part may separate the lens material from the insert. Accordingly, it may be desirable to develop alternative techniques to form ophthalmic lenses with inserts.